Add tests to ensure this issue is fixed

tests/testsuite/cargo_add/add_no_vendored_package_with_alter_registry/in/Cargo.toml

@@ -0,0 +1,5 @@
+[workspace]
+
+[package]
+name = "cargo-list-test-fixture"
+version = "0.0.0"

tests/testsuite/cargo_add/add_no_vendored_package_with_alter_registry/mod.rs

@@ -0,0 +1,56 @@
+use cargo_test_support::compare::assert_ui;
+use cargo_test_support::paths;
+use cargo_test_support::prelude::*;
+use cargo_test_support::ProjectBuilder;
+
+use cargo_test_support::curr_dir;
+
+#[cargo_test]
+fn case() {
+    cargo_test_support::registry::alt_init();
+    cargo_test_support::registry::Package::new("linked-hash-map", "0.5.4")
+        .feature("clippy", &[])
+        .feature("heapsize", &[])
+        .feature("heapsize_impl", &[])
+        .feature("nightly", &[])
+        .feature("serde", &[])
+        .feature("serde_impl", &[])
+        .feature("serde_test", &[])
+        .alternative(true)
+        .publish();
+
+    let project = ProjectBuilder::new(paths::root().join("in"))
+        .file(
+            ".cargo/config.toml",
+            r#"[source.crates-io]
+replace-with = "vendored-sources"
+
+[source.vendored-sources]
+directory = "./vendor"
+"#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "Cargo.toml",
+            r#"[workspace]
+
+[package]
+name = "cargo-list-test-fixture"
+version = "0.0.0"
+"#,
+        )
+        .build();
+    let project_root = project.root();
+    let cwd = &project_root;
+
+    snapbox::cmd::Command::cargo_ui()
+        .arg("add")
+        .arg_line("linked_hash_map --registry alternative")
+        .current_dir(cwd)
+        .assert()
+        .success()
+        .stdout_matches_path(curr_dir!().join("stdout.log"))
+        .stderr_matches_path(curr_dir!().join("stderr.log"));
+
+    assert_ui().subset_matches(curr_dir!().join("out"), &project_root);
+}

tests/testsuite/cargo_add/add_no_vendored_package_with_alter_registry/out/Cargo.toml

@@ -0,0 +1,8 @@
+[workspace]
+
+[package]
+name = "cargo-list-test-fixture"
+version = "0.0.0"
+
+[dependencies]
+linked-hash-map = { version = "0.5.4", registry = "alternative" }

tests/testsuite/cargo_add/add_no_vendored_package_with_alter_registry/stderr.log

@@ -0,0 +1,11 @@
+    Updating `alternative` index
+warning: translating `linked_hash_map` to `linked-hash-map`
+      Adding linked-hash-map v0.5.4 to dependencies.
+             Features:
+             - clippy
+             - heapsize
+             - heapsize_impl
+             - nightly
+             - serde
+             - serde_impl
+             - serde_test

tests/testsuite/cargo_add/add_no_vendored_package_with_vendor/in/Cargo.toml

@@ -0,0 +1,5 @@
+[workspace]
+
+[package]
+name = "cargo-list-test-fixture"
+version = "0.0.0"

tests/testsuite/cargo_add/add_no_vendored_package_with_vendor/mod.rs

@@ -0,0 +1,55 @@
+use cargo_test_support::compare::assert_ui;
+use cargo_test_support::paths;
+use cargo_test_support::prelude::*;
+use cargo_test_support::ProjectBuilder;
+
+use cargo_test_support::curr_dir;
+
+#[cargo_test]
+fn case() {
+    let project = ProjectBuilder::new(paths::root().join("in"))
+        .file(
+            ".cargo/config.toml",
+            r#"[source.crates-io]
+replace-with = "vendored-sources"
+
+[source.vendored-sources]
+directory = "./vendor"
+"#,
+        )
+        .file("vendor/aa/src/lib.rs", "")
+        .file("vendor/aa/.cargo-checksum.json", "{\"files\":{}}")
+        .file(
+            "vendor/aa/Cargo.toml",
+            r#"[workspace]
+
+[package]
+name = "aa"
+version = "0.0.0"
+"#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "Cargo.toml",
+            r#"[workspace]
+
+[package]
+name = "cargo-list-test-fixture"
+version = "0.0.0"
+"#,
+        )
+        .build();
+    let project_root = project.root();
+    let cwd = &project_root;
+
+    snapbox::cmd::Command::cargo_ui()
+        .arg("add")
+        .arg_line("cbindgen")
+        .current_dir(cwd)
+        .assert()
+        .success()
+        .stdout_matches_path(curr_dir!().join("stdout.log"))
+        .stderr_matches_path(curr_dir!().join("stderr.log"));
+
+    assert_ui().subset_matches(curr_dir!().join("out"), &project_root);
+}

tests/testsuite/cargo_add/add_no_vendored_package_with_vendor/out/Cargo.toml

@@ -0,0 +1,8 @@
+[workspace]
+
+[package]
+name = "cargo-list-test-fixture"
+version = "0.0.0"
+
+[dependencies]
+aa = "0.0.0"

tests/testsuite/cargo_add/add_no_vendored_package_with_vendor/stderr.log

@@ -0,0 +1 @@
+error: the crate `cbindgen` could not be found in registry index.

tests/testsuite/cargo_add/mod.rs

@@ -1,5 +1,7 @@
 mod add_basic;
 mod add_multiple;
+mod add_no_vendored_package_with_alter_registry;
+mod add_no_vendored_package_with_vendor;
 mod add_normalized_name_external;
 mod add_toolchain;
 mod build;